Soft front brake

[miatamarty]

I rebuilt the front master cylinder. Bled it quite a bit. No air bubbles coming out at caliper. Still have a very soft lever, comes almost back to the grip. This bike sat for a long time kind of a barn find that was brought back to life. I'm thinking I might have some frozen pistons in the caliper. The soft lever is due to the caliper flexing. My Lightening has a nice firm lever in comparison. Any thoughts? I did order a rebuild kit from St Paul HD.

 

[Kurlon]

The master is the high point in the system, so I'd try some bleeding there next. My normal technique is to pop the resi cap off, make sure the resi is around half full, and have some paper towels handy, this can cause spurts/splashes. Give the lever four or five slow full squeezes and slow returns. Next, switch to a slow full squeeze but then let the lever go so it snaps back as fast as it can. When it snaps back watch the resi, you should have fluid flow in, possibly a fountain (splash warning!), and hopefully some air bubbles show up after two or three snaps. Alternate between slow returns and snaps, as the bubbles stop, slow pumps for a bit to get air collected at the top, snaps to coax it out. It can also help to 'twang' the brake line in a few spots to encourage stuck bubbles to travel up.

The other way to do this, use the banjo bolt on the master as a bleeder, resi cap back on, wrench on the bolt with paper towels to catch the spray around the banjo. A few slow full pumps to again get the bubbles collected at the high point, full squeeze, hold, and then crack the banjo bolt loose. You'll hopefully hear air then spurting, tighten it once the fart goes liquid. Repeat a few times and see if that gets more air out.

 

[Pushr0d]

Also check to see if the caliper pucks are stuck to the seals and being pulled back

Easiest to see if you take the caliper off and put a 1/2" or so piece of wood in between to keep the pucks from coming out completely. Slowly squeeze the lever to extend the pucks. Seals should stay in place. You'll find not all the pucks extend equally - it can get a bit fiddley. A couple small C-clamps can be very useful.

When 'fully extended', give the pucks a good clean with brake cleaning fluid.

When you've done that, hang the caliper straight down on the hose, and press the pucks all the way back into the caliper. As Kurlon mentions, careful of the mess at the reservoir. If your level is topped off when the pucks are much extended, it'll overflow when you press them fully home.